Iron deficiency anaemia (IDA) is one of the most common reasons for gastro referrals.

In adults, especially:

men
postmenopausal women

IDA should be assumed to be:

👉 occult GI blood loss until proven otherwise

Your job is to:

confirm iron deficiency
look for the cause
exclude cancer
treat safely

Not just prescribe iron and discharge.

✅ First principle (most important)

Always ask:

Why is this patient iron deficient?

Because:
Iron deficiency is a sign, not the diagnosis.

Never stop at “give iron”.

✅ Step 1 – Confirm it is true iron deficiency

Don’t assume from Hb alone.

Typical blood results

FBC

Low Hb
Low MCV (microcytic)
Low MCH

Iron studies

Low ferritin (most important)
Low iron
High TIBC

Ferritin is the key test.

👉 Low ferritin = iron deficiency (until proven otherwise)

Important caveat

Ferritin is an acute phase reactant.

If CRP high:
Ferritin may look “normal”

Still consider IDA if clinical picture fits.

✅ Step 2 – Decide who needs urgent investigation

This is the most important clinical decision.

🚨 Higher risk patients (investigate urgently)

Men
Postmenopausal women
Age >50
Weight loss
Change in bowel habit
Rectal bleeding
Family history cancer
Severe anaemia
Recurrent IDA

Think:
👉 GI malignancy until excluded

These patients usually need:
👉 OGD + colonoscopy

Not just iron tablets.

✅ Step 3 – Look for common causes (practical thinking)

In the NHS, most causes are:

Most common

Colorectal cancer
Gastric cancer/ulcer
Coeliac disease
IBD
NSAID gastritis
Menstrual loss (premenopausal)

Less common

Malabsorption
Angiodysplasia
Haemorrhoids (rarely severe enough alone)
Dietary deficiency alone (uncommon in UK adults)

Do not blame “diet” without investigating.

✅ Step 4 – First-line investigations

Bloods

FBC
Iron studies
CRP
Coeliac screen (tTG)

Never forget coeliac.

Very commonly missed.

Endoscopy (core investigations)

Most adults:

👉 OGD + colonoscopy

Because:
Bleeding source could be anywhere.

This is standard practice.

Special situations

Young menstruating women

Often:

trial iron first
investigate only if severe/persistent/red flags

Frail elderly

Balance benefit vs risk

Individualise

✅ Step 5 – What each test is looking for

Helps explain to patients too.

OGD

ulcers
gastritis
gastric cancer
coeliac

Colonoscopy

colorectal cancer
polyps
IBD
angiodysplasia

Together they identify most causes.

✅ Step 6 – Treat the anaemia as well

Investigation AND treatment together.

Iron replacement

Oral first line

ferrous sulphate/fumarate
once daily or alternate days

Common side effects:

constipation
nausea

IV iron

Consider if:

intolerance
malabsorption
severe anaemia
rapid correction needed

Transfusion

Only if:

symptomatic
haemodynamically unstable
very low Hb

Don’t transfuse just because Hb is low.

✅ Practical ward scenarios

Scenario 1

65-year-old man, Hb 85, ferritin 8
→ urgent OGD + colonoscopy

Scenario 2

Young woman, heavy periods, Hb 105
→ trial iron first

Scenario 3

IDA + diarrhoea + bloating
→ check coeliac → OGD biopsy

Scenario 4

IDA + weight loss + change in bowel habit
→ urgent cancer pathway

Scenario 5

Normal scopes but persistent IDA
→ consider small bowel/bile acid/pancreatic causes

✅ When to refer to gastro

Refer if:

male or postmenopausal with IDA
unexplained IDA
recurrent IDA
red flags
positive coeliac screen
persistent symptoms

Do not discharge unexplained IDA without investigation.

❌ Common junior mistakes

Prescribing iron without finding cause
Blaming diet
Forgetting coeliac screen
Not scoping older adults
Assuming haemorrhoids are the cause
Ignoring recurrent anaemia

Remember:
IDA may be the first sign of cancer.

✅ Simple ward algorithm

When you see iron deficiency:

Confirm ferritin low
Any red flags?
OGD + colonoscopy (most adults)
Start iron
Follow up Hb

Simple and safe.

✅ Take-home concept

In adult men and postmenopausal women, iron deficiency anaemia is GI blood loss until proven otherwise.
Investigate first, then treat.

This mindset prevents missed cancers.